The growth and fructan contents of plants of Vernonia herbacea (Vell.) Rusby regenerated from fragments of the underground organ (rhizophore) were analysed during two developmental cycles. When cultivated away from their natural ecosystem, these plants went through the same phenological phases as those naturally grown in the cerrado. The first aerial shoots started developing from initial fragments before the new underground system, the former acting as the main metabolic sink for the fructan present in the initial fragments. The new rhizophores started to develop by the sixth month, as photosynthates were transformed into fructans. Growth parameters measured reached higher values in the second growth cycle, exhibiting growth curves synchronized with those obtained for fructan contents in the new rhizophores. Fructo-oligosaccharides were available mostly during the period of fast growth of aerial organs whilst the fructo-polysaccharides were reduced. Fructan variation indicates that these compounds are metabolized during development. Additionally, the rapid growth, intense production of rhizophores and high fructan content make Vernonia herbacea a promising source of fructan for commercial use.

Chamaegigas intrepidus Dinter (syn. Lindernia intrepidus (Dinter) Oberm.) is a poikilohydric aquatic plant that lives in rock pools on granitic outcrops in Central Namibia. The pools are only filled intermittently during the summer rains, and the plants can pass through 15–20 rehydration/dehydration cycles during a single wet season. Rehydrated plants also have to cope with substantial diurnal fluctuations in the pool pH as a result of photosynthetic CO2 uptake. We have used in vivo31P NMR spectroscopy to investigate the effect of external pH and dehydration (low water potential) on intracellular pH in the roots and submerged leaves of C. intrepidus. Increasing the external pH from 6 to 10 had no effect on the steady state cytoplasmic and vacuolar pH values of submerged leaves, but caused a slight alkalinization of the root cytoplasm. Similarly dehydration with PEG-600 at either pH 6 or pH 10 had no effect on the cytoplasmic pH of the leaves, but it did cause a small alkalinization of the leaf vacuoles at pH 10. These results imply an unusually effective regulation of intracellular pH, consistent with the adaptation of C. intrepidus to the extreme environmental conditions of its habitat. The NMR analysis also showed that dehydration had no effect on the inorganic phosphate and phosphocholine pools, and this was taken to indicate that the cell membranes were well protected from the effects of the low water potential.

New Phytologist145 (2000), 1–3

In the January 2000 issue of New Phytologist, we published the forum article entitled ‘Cadmium for all meals – plants with an unusual appetite’ by U. Krämer. Since its publication, it has been brought to our attention that an error was introduced during typesetting. In the text several instances of concentrations are erroneously presented as mg−1: these should be kg mg−1.

New Phytologist145 (2000), 367–421

In the March 2000 issue of New Phytologist, we published the Tansley review entitled ‘Numerical and physical properties of orchid seeds and their biological implications’ by J. Arditti and A. K. A. Ghani. Since its publication, it has been brought to our attention that an error was introduced during typesetting. On p. 391, Eqn 5, the horizontal line above the right side of the equation should form a square root sign.

We apologize to the authors and to our readers for these mistakes.

This study investigates the phytotoxicity of ozone during periods of natural frosts following long-term fumigation. Heather (Calluna vulgaris (L.) Hull.) plants were fumigated with ozone for 6 months at 70 nl l−1, for 8 h d−1, 5 d a week in open-top chambers. Natural frosting occurred within the chambers towards the end of this period (5–27 December 1995). Plant responses to the ozone/natural frosting episode were recorded in January 1996. We show conclusively that naturally occurring frost exposure results in increased damage and mortality for ozone-treated plants, which could have important implications for the function of heathland ecosystems.

Possible interactions of two synthetic plant-growth retardants during the short-term response of Brassica rapa L. ssp. oleifera (DC.) Metzger plants to low root-zone temperature were investigated by pretreating with mefluidide or paclobutrazol. Water and solute transfers were studied by measuring xylem sap volume flow (under root pressure exudation) and ion flow from the roots. Relations with nitrate uptake rate were also considered. Root pretreatment with paclobutrazol strongly restricted the cold-inducible processes which normally restore water and solute flow from the root xylem. Paclobutrazol decreased the rates of nitrate uptake and exudation flow from the root xylem (principally by reducing root hydraulic conductivity) with dramatic consequences for ion flow, especially that of nitrate.

The effects of root ABA pretreatment on plant response to root cooling were then studied separately or in association with a pretreatment with paclobutrazol. Despite a slight decrease in nitrate uptake rate, ABA pretreatment of the roots enabled the plant to develop rapid mechanisms for adaptation to cold constraint at the root level. Moreover, this action of exogenous ABA greatly reduced the effect of a simultaneous paclobutrazol pretreatment and partly restored water and solute flows.

Thus, the improvement of plant resistance to cold conditions brought about by treatments with mefluidide and paclobutrazol (previously shown in long-term experiments) cannot simply be explained by their short-term effects.

This light- and electron-microscope study of four species of Sphagnum reveals that stem elongation involves meristematic activities unique to the group and hitherto unrecognized. The internal tissue of the mature stem arises by the concerted activity of an apical (primary) and a subapical (secondary) meristem. The primary meristem comprises the immediate derivatives of the single apical cell. Following a small number of divisions, the primary derivatives differentiate into highly vacuolate parenchymatous cells with a storied arrangement. Subsequently, the large vacuoles are replaced by numerous small vacuoles and the cells then divide repeatedly, by transverse septa, producing files of about nine short cells. Finally, ninefold elongation of these secondary cells is responsible for extension growth of the main stem below the mature capitulum. An early step in primary differentiation is the confinement of pre-existing plasmodesmata to distinct pitted areas. Further enlargement of the cells during primary and secondary differentiation involves the thickening of non-pitted wall areas, followed by expansion and thinning out, while the pitted areas remain virtually unchanged. A cortical array of microtubules is regularly found in association with non-pitted wall areas, while the unexpanded pitted areas are associated with smooth endoplasmic reticulum showing continuity with desmotubules. Though sharing much the same cytology as the conducting cells in bryoid mosses, in terms of their development the central stem cells in Sphagnum are not homologous with those of other mosses. The unique mode of stem development may be an important factor in the ecological success of Sphagnum.

Potted subterranean clover (Trifolium subterraneum) plants of different ages were exposed to 70 nl l−1 ozone for 6 h, either during the light or during the dark period in a laboratory-based climate chamber. There was limited visible leaf injury on plants which were 14–20 and 28–34 d old and no significant decrease in biomass after daytime ozone exposure. The oldest leaves of 22–26 d old plants exhibited severe visible injury, which was associated with a significant reduction in biomass in 24–26 d old plants. Thus, ozone-induced visible injury of different magnitude developed in all plants, but was associated with biomass reduction only during a limited period of the plant's life-span. Apart from modifying ozone uptake by plants, climatic conditions are important as growth modifiers. It is suggested that subterranean clover plants of defined developmental stages should be used in bioindication of ozone. Night ozone exposure injured significantly fewer leaves than day exposure. However, some leaves developed visible injury even after night ozone exposure. Night uptake of ozone may be of more importance in northern than in central and southern Europe, because summer nights are short and, for a certain period, never completely dark.

Solution culture studies have demonstrated that apoplasmic iron (Fe) deposited in the roots of dicotyledonous and graminaceous plants can be mobilized to improve plant iron status in conditions of limited Fe supply. The present study investigated the formation of the apoplasmic Fe pool in dicotyledonous (soybean and cucumber) and graminaceous (wheat) plants in a pot experiment. The pots had three compartments such that plants could take up Fe and other nutrients from two calcareous soils treated with different Fe forms without their roots touching with soil directly. In this way overestimating Fe accumulation in root apoplasm was avoided. The results showed that while the root d.wt of wheat did not vary when soils were supplied with different Fe resources, the root d. wt of soybean and cucumber supplied with FeEDTA decreased compared with the control (without Fe treatment). Supplying FeEDTA in the side compartment increased shoot d. wt and Fe concentration in shoots of all species. However, supplying Fe(OH)3 had no effect on shoot d. wt or Fe concentration in the shoots of any species. Soybean and cucumber accumulated little or no Fe in the root apoplasm in controls or in Fe(OH)3 treatments. By contrast, a large amount of Fe was deposited in the root apoplasm of wheat grown in similar conditions. Remarkably, when FeEDTA was supplied in the soils, large apoplasmic iron pools were formed in the roots of all three species. Therefore, in dicotyledonous plants grown on calcareous soils, little or no apoplasmic iron pool forms, because there is not enough available Fe in the soil solution and the plants have little ability to mobilize Fe3+ in the soil. By contrast, a larger apoplasmic iron pool could form in graminaceous plants at lower concentrations of available soil-Fe possibly by enhancing the release of phytosiderophores which could mobilize Fe3+ in the soil and then transfer the Fe3+-complexes to the root apoplasm.

John Innes Centre, Norwich, UK, June 2000

Genomics research involving legumes, an area that is attracting major funding, has two distinct branches – work involving model species, and work involving crops. This meeting aimed to stimulate communication between these two groups. The major research areas covered included leaf, flower and seed development, establishment of symbioses, pathogen interactions and applied aspects (from the conservation of legume ecotypes to products required by the market).

The number of papers submitted to New Phytologist by authors working in North America has increased significantly in recent years. We are now able to offer those authors a better service because, from this month, they will be able to submit their papers direct to our new USA Office – this is being supervised by one of our Editors, Richard Norby, and is located at Oak Ridge, Tennessee:

New Phytologist USA Office, Oak Ridge National Laboratory, Bldg 1059, PO Box 2008, Oak Ridge, TN 37831-6422, USA. Tel: +1 423 576 5261. Fax: +1 423 576 9939. E-mail: [email protected].

Following a 3-wk pretreatment with 150 mM NaCl, Sorghum plants were able to survive exposure to 300 mM NaCl, a lethal concentration for nonpretreated plants. This response is termed salt adaptation. Although the population was initially homogeneous, Na-includer and Na-excluder individuals coexisted after the achievement of the salt-adaptation response, and a large diversity in size of the seeds produced was observed at the end of the life cycle. Offspring of salt-adapted plants were exposed to a new salt-adaptation treatment. Even in the absence of selection, the proportion of Na-excluder individuals in the progeny was significantly increased. Offspring germinated from small seeds differed significantly from plants first-exposed to a salt-adaptation treatment, whereas offspring from large seeds displayed intermediate characteristics. This suggests that some of the adaptive changes were transmitted through embryo imprinting. The importance of this phenomenon for emergence of a newly adapted ecotype is discussed.

Barley yellow dwarf virus (BYDV) causes significant losses in yield and in overwintering ability of winter cereals. Mechanisms by which the physiology of plants is affected by the virus are not clear. To see how carbohydrates in the crown of winter cereals were affected by BYDV, fructan isomers of degree of polymerization (DP) 3–5, fructan DP>6 and the simple sugars, glucose, fructose and sucrose, were measured before and during cold hardening in three oat (Avena sativa L.) cultivars, ‘Wintok’, ‘Coast Black’ and ‘Fulghum’. On a fresh weight basis fructan DP>6 decreased by 50% in infected ‘Wintok’ and ‘Coast Black’ and by 25% in ‘Fulghum’. Two DP3, one DP4 and one DP5 isomer were significantly higher than non-infected controls. The percentages of simple sugars in infected crowns were significantly higher than controls in all three cultivars in every week except the first week of hardening. Crude enzyme extracts from BYDV infected plants incubated with sucrose suggested higher invertase and lower sucrose-sucrosyl transferase activity. When incubated with 1-kestose and neokestin, no significant difference was found in fructose fructosyl transferase or in hydrolase activity. The activity of unidentified enzymes catalysing the synthesis of larger (DP>5) fructan was altered by BYDV. The decrease of carbohydrates in the crown induced indirectly by BYDV may alter the plant's capacity to regenerate tillers in the spring. The ability of plants to prevent or tolerate carbohydrate fluctuations induced by BYDV infection may be an important genetically regulated characteristic for developing virus-resistant cultivars.

Ca2+ was localized in chemically injured internodal cells of the characean alga Nitella flexilis (L.) Ag. using alizarin red and antimonate precipitation. The presence of Ca2+ in the antimonate precipitates was verified by X-ray analysis and EGTA chelation. Callose-containing amorphous wound walls were induced by 0·1 mm chlortetracycline (CTC) and cellulosic fibrillar wound walls were induced by 50 mm CaCl2. Numerous precipitates were found in the amorphous wound walls and in the adjacent cytoplasm. Precipitates were mainly localized in single membrane-bound cisternae, probably of the endoplasmic reticulum, which accumulate at the wound and become a component of the amorphous wound wall via membrane fusion. In fibrillar wound walls, which do not contain membranous residues, precipitate density was significantly lower and similar to that in the secondary cell wall.

The data suggest that the high Ca2+ content of amorphous wound walls is due to incorporation of cytoplasmic Ca2+ stores. The possible function of amorphous wound walls in maintaining cellular Ca2+ homeostasis is discussed.

The gradients in photosynthetic and carbohydrate metabolism which persist within the fully expanded second leaf of barley (Hordeum vulgare) were examined. Although all regions of the leaf blade were green and photosynthetically active, the basal 5 cm, representing approximately 20% of the leaf area, retained some characteristics of sink tissue. The leaf blade distal from the leaf sheath exhibited characteristics typical of source tissue; the activities of sucrolytic enzymes (invertase and sucrose synthase) were relatively low, whilst that of sucrose phosphate synthase was high. These regions of the leaf accumulated sucrose throughout the photoperiod and starch only in the second half of the photoperiod whilst hexose sugars remained low. By contrast the leaf blade proximal to the leaf sheath retained relatively high activities of sucrolytic enzymes (especially soluble, acid invertase) whilst sucrose phosphate synthase activity was low. Glucose, as well as sucrose, accumulated throughout the photoperiod. Although starch accumulated in the second half of the photoperiod, a basal level of starch was present throughout the photoperiod, by contrast with the rest of the leaf. The 14CO2 feeding experiments indicated that a constant amount of photosynthate was partitioned towards starch in this region of the leaf irrespective of irradiance. These findings are interpreted as the base of the leaf blade acting as a localized sink for carbohydrate as a result of sucrose hydrolysis by acid invertase.

Cell division was examined during leaf initiation in the slow-to-green mutant of Lolium temulentum L. to test the hypothesis that the cell cycle in the leaf primordium is a key regulator of the well characterized reduction in final leaf length in the mutant compared with that of the wild type. The cell doubling time (cdt, by colchicine method) was substantially longer in the youngest leaf primordium (YLP) of the mutant (107 h) than in the wild type (43 h) although the duration of the most rapid cell cycle (cc, by percentage labelled mitoses method) was between 18–20 h in each. As a consequence, the proportion of rapidly proliferating cells was only 20% in the mutant compared with 47% in the wild type. The size of the shoot apical meristem and the plastochron were similar between genotypes which indicates that the shoot meristem was largely buffered from the effects of the mutation. Mitotic cell area was also similar in the YLP of both genotypes. However, as the leaf elongated, mitotic cell area and interphase cell size were significantly larger in the mutant compared with the wild type. This change was coupled with a reduced number of cells per unit length of leaf in the mutant. The data are consistent in showing that the proportion of rapidly proliferating cells in the YLP (but not the rate of cell division) is a key parameter which influences growth of the leaf.

Sucrose[ratio ]sucrose fructosyltransferase (SST) activity was partially purified from whole shoots of Lolium rigidum by a combination of affinity chromatography, gel filtration and anion-exchange chromatography. The SST activity co-eluted with some fructan[ratio ]fructan fructosyltransferase (FFT) and invertase activities and consequently the partially purified preparation was termed the fructosyltransferase (FT) preparation.

The SST-like activity in the FT preparation was purified 214-fold and had an apparent molecular mass of 84000. The FT preparation contained several peptides with an apparent pI of 4·6–4·7. When assayed with sucrose concentrations up to 600 mM, the FT preparation synthesized 1-kestose at all concentrations, and synthesized 6-kestose at concentrations of 150 mM and greater. The Km of 1-kestose production was 0·2 M. When the FT preparation was assayed at a concentration of activity approximately half that measured in fresh tissue with 100 mM sucrose, 1-kestose, or 6G-kestose as substrates, fructans of degree of polymerization (DP) [les ]5 were synthesized.

A partially purified FFT activity, free of SST and invertase activities, which synthesized β-2,1-glycosidic linked oligofructans of DP [les ]6, was combined in vitro with the FT preparation (FFT-FT preparation) to give a ratio of SST[ratio ]FFT activities similar to that measured in crude enzyme extracts from L. rigidum. The FFT-FT preparation synthesized oligofructans when assayed with 100 mM concentrations of sucrose, 1-kestose or 6G-kestose, but was not able to synthesize fructans of DP [ges ]6 even after extended assays of up to 10 h. The FFT-FT preparation was also assayed with 100 mM sucrose with small amounts of concentrated sucrose added periodically during the assay to maintain the substrate concentration. In this assay, the FFT-FT preparation synthesized fructans up to an apparent DP of 17 or greater. The fructans of DP [ges ]6 synthesized in the assay appeared to form two molecular series containing both β-2,1- and β-2,6-glycosidic linked fructosyl residues with terminal or internal glucosyl residues. The apparent rate of SST activity in the assay of the FFT-FT preparation was greater than that measured in a similar assay of the FT preparation alone which did not result in fructans with DP [ges ]6. It was concluded that the FFT-FT preparation, when assayed with a continual supply of sucrose, contained a factor which promoted synthesis of fructans of DP [ges ]6 and synthesis of β-2,6-glycosidic linkages between fructosyl residues.

The presence and variation of activity of the type 1 ribosome-inactivating protein saporin has been evaluated in cultured roots of the soapwort Saponaria officinalis. Results from western analysis and in vitro protein synthesis inhibition indicate that saporin production is increased in senescing cultures, reaching a maximum value during the late stationary phase. Accordingly, cultures treated with the senescence-related hormone abscisic acid show a significant increase in saporin activity, independently from the culture growth phase. Stress conditions, such as the presence of hydrogen peroxide in the culture medium, had no effect on the modulation of enzymatic activity. The putative regulation of saporin production by abscisic acid and its possible role in accomplishing the ageing programme is discussed.

Changes in leaf water content, night-time accumulation of malic (Δ-malate) and citric acid (Δ-citrate) and phosphoenolpyruvate carboxylase (PEPC, EC 4 . 1 . 1 . 31) activity were followed for 60 d after germination in well watered and salt-stressed plants of the facultatively halophytic ephemeral Mesembryanthemum crystallinum L. To separate the effects of development, salt stress and water deficit on crassulacean acid metabolism (CAM) induction plants were stressed initially 10 d after germination and then successively at 1-wk intervals (five sets). Related to dry mass or organic matter (i.e. dry mass corrected for the mass of inorganic ions) water content started to decrease during the late embryonal phase of the life cycle. Water content on a dry mass basis was always lower in salt-stressed than in well watered individuals. However, on an organic matter basis no difference was detectable. This indicated that salt treatment did not reduce leaf water content but falsified the basis (dry mass). Increases in leaf succulence and in pressure potential prevented long-term water deficit in well watered and in salt-stressed plants. Instead, these changes displayed enhanced vacuolisation, which is an essential prerequisite for the development of CAM. The end of that differentiation process might allow the initiation of nocturnal malic acid accumulation in a threshold response. At the onset of each salt treatment, short-term water deficits occurred due to an incomplete osmotic adaptation independent of plant age. As Δ-malate only appeared when plants were c. 35 d old this water deficit was unlikely to be a decisive CAM-inducing factor. About 2 wk after germination water content began to decline during the light periods in plants of all treatments. This pattern disappeared again when CAM had been fully established. Daytime transpirational water loss is therefore unlikely to be the decisive factor because it failed to induce the metabolic shift in young plants. Environmental stress (e.g. salt or drought) can therefore only induce Δ-malate when leaf and plant differentiation has reached a certain stage.

The population dynamics of perennial crop plants are influenced by numerous factors, including management practices. Conditions in the field vary from year to year, and matrix population models are useful for evaluating population behaviour in relation to environmental variability. In Missouri, the stand persistence of birdsfoot trefoil (Lotus corniculatus), a perennial legume, is often limited by disease and poor seed production. A stage-based, matrix population model was developed to evaluate the population dynamics of birdsfoot trefoil in relation to clipping treatment. The plant growth stages represented in the model were seeds, seedlings, mature vegetative and reproductive plants. Two phases of population growth were evaluated in clipped and unclipped stands. Establishment-phase populations were characterized by relatively high mortality and low reproduction. Elasticity analysis indicated that growth of these populations was most sensitive to the survival of vegetative plants. Mature vegetative plants and seeds comprised the majority of surviving individuals in clipped and unclipped populations, respectively; however, establishment-phase populations under both management treatments tended toward extinction. Populations in the post-establishment phase of growth were characterized by relatively low mortality and high reproduction. Population growth in this phase of growth was most sensitive to seed production, and most individuals in these populations were at the seed stage.